Sequence Stratigraphic Controls from Complex Reservoir Architecture in Fluvial-Dominated Deltaic and Lowstand Valley-Fill Deposits in the Woodbine Group, East Texas Field

William A. Ambrose, Tucker F. Hentz, Fred P. Wang, Florence Bonnaffe, Robert G. Loucks, and Leonard F. Brown
Bureau of Economic Geology, Austin, TX

Analysis of >1,500 ft (>450 m) of 30 whole cores and closely spaced log sections with approximately 500 wells in the Woodbine Group in East Texas field and adjacent areas indicates that the sandbody architecture in the field is more complex than inferred from previous studies. Extreme sandbody heterogeneity in the lower Woodbine Group is controlled by the fluvial-dominated deltaic depositional architecture, with dip-elongate distributary-channel sandstones pinching out over short distances (typically <500 ft [<150 m]) into delta-plain and interdistributary-bay siltstones and mudstones. This highstand section is truncated in the northern and western part of the field by a thick (commonly 100- to 150-ft [30- to 45-m]) lowstand, valley-fill succession composed of bedload fluvial deposits of multistoried, coarse-gravel and coarse-grained sandy beds. This valley-fill section in some areas in East Texas field directly overlies muddy, delta-front deposits, from which as much as 100 ft (30 m) of lowstand incision is inferred. Correlation with the Woodbine succession in the East Texas Basin indicates that these highstand and lowstand deposits represent the basal three, fourth-order sequences of the Woodbine Group which comprises a maximum of 14 cycles.

Previous studies of the Woodbine Group inferred well-connected, laterally continuous sheet sandstones in a wave-dominated deltaic and barrier-strandplain setting. This wave-dominated deltaic model is inappropriate, and a full understanding of reservoir compartmentalization, fluid flow, and unswept mobile oil in East Texas field should consider the fluvial-dominated deltaic and lowstand valley-fill sandbody architecture.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas